1. Field of the Invention
This invention relates to an electrostatic chuck for attracting and holding a workpiece by electrostatic attraction forces and more particularly, to an electrostatic chuck as a support table for holding workpieces such as semiconductor wafers or glass substrates in the processes of manufacturing semiconductor devices and liquid crystal substrates.
2. Background Art
In the conventional semiconductor manufacture process including such steps as etching of a semiconductor wafer, deposition of a thin film on a semiconductor wafer and imagewise exposure of photoresist, an electrostatic chuck is often used for holding the semiconductor wafer.
One typical electrostatic chuck includes an electrode disposed between an insulating substrate and a dielectric layer for electrostatic attraction, the upper surface of the dielectric layer serving as an attracting surface. While a workpiece, typically a semiconductor wafer is rested on the attracting surface, a voltage is applied between the electrode and the semiconductor wafer to develop Coulomb forces or Johnson-Rahbek forces due to inductive polarization, for attracting and holding the wafer. Also known in the art is a dipole type electrostatic chuck comprising a plurality of electrodes formed between an insulating substrate and a dielectric layer for electrostatic attraction wherein a voltage is applied between the electrodes for attracting and holding a wafer resting on the attracting surface.
The dielectric layer used in these electrostatic chucks must meet minimized sliding wear upon mounting and dismounting of wafers, and resistance to corrosion by corrosive gases used in various treatments. The materials employed in the art as satisfying such requirements include insulating ceramics having high wear resistance and corrosion resistance such as alumina and aluminum nitride. However, alumina can be crazed and distorted when sprayed thick, giving rise to delamination and other problems. To enhance the dielectric strength of sprayed alumina coatings, pores in the sprayed coating must be sealed. Through the sealing treatment, organic fills are introduced into pores which in turn, become susceptible to etching, generating unwanted particles. Due to low dielectric strength, ceramics must be deposited to a greater thickness, which leads to a lower attractive force, which in turn, requires to increase a voltage in order to produce a certain attractive force, inviting a vicious circle. The increased thickness also gives rise to the problem that the adhesive strength of sprayed coating is reduced by the stresses associated with thermal expansion.